A cationic polymerization initiator has a function to polymerize cationically polymerizable compounds, such as epoxy compounds, by generating an acid upon receiving energy, such as light or heat. A photo-acid generator has a function to change the solubility of a resist composition into a developer by generating an acid upon receiving light energy. Various onium salts have been used as a cationic polymerization initiator and photo-acid generator, and as the anion component of the onium salts, it has been known that antimony hexafluoride anion (SbF6−) has an excellent acid-generating function, exhibiting superior effects.
However, the toxicity of antimony hexafluoride has been regarded as a problem; therefore, alternatives have been studied. For instance, an onium salt compound prepared by using a fluorine-substituted tetraphenyl boric acid anion represented by B(C6F5)4− is disclosed in Patent Document 1. Further, Patent Document 2 discloses B(C6F5)4− and B(C6F4OCF3)4−, which are fluorine-substituted tetraphenyl boric acid anions, as anions of an onium compound functioning as a photo-initiator, while Patent Document 3 discloses B(C6F5)4− and B(C6F4OCF3)4−, which are fluorine-substituted tetraphenyl boric acid anions, as anions of an onium compound functioning as a cationic initiator.
Furthermore, Patent Document 4 and Patent Document 5 disclose techniques in which an aromatic sulfonium salt and an aromatic sulfonium salt are used as a photo-polymerization initiator and photo-acid generator. Described therein as the anion of the aromatic sulfonium salt is tetraaryl borate.    Patent Document 1: Japanese Unexamined Patent Application Publication No. H 6-184170    Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-526391    Patent Document 3: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-522432    Patent Document 4: Japanese Unexamined Patent Application Publication No. 2000-186071    Patent Document 5: Japanese Unexamined Patent Application Publication No. 2005-263796